1. Field of the Invention
The present invention relates to the recovery of cobalt catalyst values from a process stream in the manufacture of N-acyliminodiacetic acids. More particularly, the present invention relates to the recovery of cobalt catalyst values from a process stream in the manufacture of N-acyliminodiacetic acids by a process involving ion-pair extraction.
2. Prior Art
U.S. Pat. No. 3,766,266 discloses a process for manufacturing N-acylaminoacids involving reacting an aldehyde with an amide in the presence of carbon monoxide and of a carbonylation catalyst. The patent also discloses that the reactants, i.e., the aldehyde and the amide, can be formed in situ. Suggested catalysts useful in the carbonylation reaction include the transition elements of iron, cobalt and nickel.
U.S. Pat. No. 533,500 discloses that N-acyliminodiacetic acids can be obtained by reacting formaldehyde, or a formaldehyde generator, with an amide, or an amide generator, and with carbon monoxide. The carbonylation catalysts suggested by the prior art include metals of Group VIII of the periodic chart, and more particularly, cobalt. A specifically disclosed cobalt catalyst is dicobaltoctacarbonyl. There is no disclosure in the patent of an effective and economical procedure for recovering the cobalt catalyst at high levels of purity from the reaction product.
U.S. Pat. No. 4,567,284 discloses recovery of a cobalt catalyst by solvent extraction hydrometallurgy. Certain N-alkylalkanohydroxamic acids in a hydrocarbon solvent are suggested to be used to extract the cobalt from an aqueous solution, separating the hydrocarbon solvent cobalt-containing organic phase and recovering the organic phase. While N-alkylalkanohydroxamic acids are known as extractants, they also are known to be chelating agents. The mode of action of hydroxamic chelating agents is to chelate the Co.sup.+2 ion in order to form an organic soluble species. Such species can be stripped from the organic solution using aqueous ammonia. Unfortunately, when hydroxamic chelating agents are applied to the reaction product of U.S. Pat. No. 533,500, it was found that N-acetyliminodiacetic acid competes effectively as a chelating agent with hydroxamic acid for cobalt (Co.sup.+2), and thereby renders the use of hydroxamic acids unsatisfactory in recovering cobalt in the presence of N-acetyliminodiacetic acid.